1. Field of the Invention
The present invention relates to a photographic film cassette and more particularly to a photographic film cassette in which a leading end of a photographic film is advanced by rotation of a spool to the outside of the photographic film cassette after a cover of the cassette has been opened.
2. Description of the Related Art
In U.S. Pat. Nos. 4,834,306 and 4,832,275, there are disclosed photographic film cassettes in which a photographic film is completely contained, in the form of a roll, in a cassette shell. When a spool is rotated in the cassette shell, the leading end of the film is advanced out of the cassette shell.
The cassette shell has ridges or the like formed on an inside surface thereof to restrict loosening of the roll of photographic film. A separation claw is formed on the innermost portion of the film passage mouth integrally with the inside surface of the cassette shell so as to contact the outermost turn of the roll of the photographic film. When the roll of photographic film rotates together with the spool and the leading end reaches a position proximate the film passage mouth, the leading end is peeled from the roll by the separation claw and advanced through the film passage mouth to the outside of the cassette shell.
In addition to the film advancing function, photographic film cassettes which are provided with an openable cover member so as to prevent ambient light from entering through a film passage mouth are also known, as in U.S. application Ser. No. 07/548,520 (corresponding to Japanese Laid-open Publication No. 3-37645) .
However, such a known cover is merely a plate attached by a hinge to a cassette shell. Accordingly, the known cover can be easily opened due to vibrations and impact occurring during transportation from the factory. Also, when conventional photographic film cassettes are subjected to high temperatures, the photographic film acquires a strong curling tendency. In this case, the separation claw cannot reliably peel off the leading end from the roll of photographic film, thus causing the spool to idly rotate together with the roll of photographic film. Even when the separation of the leading end is successful, the curled leading end of the film may enter into a gap between the cassette shell and the cover member.